Update: This issue has been resolved. I recommend bookmarking the Messenger service status page. If you’re having problems connecting to the Messenger service, that’s the first place to check.
If you’re having problems logging into Messenger I recommend going to this page and checking the service status. This is where our Operations teams posts notifications about any service impacting outages or problems.
And right now they are working on a problem. Check http://messenger.msn.com/Status.aspx for the latest updates.